This is quick post to highlight a technote that some people may not be aware of.

When you try and upgrade TCR 2.1 to 2.1.1, this may fail at the "TCRCore_Upgrade" step of the install. You can confirm this by checking the Installation logs, the error message at the end of the installer will tell you which ones to look at and where they can be found.

This issue occurs when your 2.1 environment has multiple interim fixes installed. The 2.1.1 install scripts are only specifically looking for IF1 and IF2, so anything after that will cause the installer to fail. You need to amend an XML file in the 2.1.1 installer to tell it to look for the later Interim Fixes as well. Specific details and the steps on resolving this can be found in this technote -